The present invention relates, in general, to the art of pipe organs, and more particularly to a compact pipe organ wherein the size and expense of conventional organs is greatly reduced without sacrificing the unique quality of sound produced by such organs.
As is well known, a pipe organ produces unique and characteristic sound qualities which make it one of the most desirable musical instruments. These sound qualities are due in part to the complexity of the musical tones produced by each organ pipe, for each pipe has a particular structure which gives it its own characteristic harmonic structure, its own speech characteristic, its own way of starting and stopping, and its own response to pressure changes caused, for example, by tremulant devices. Thus, when a note is produced by an organ pipe, the pipe, in starting, goes through different tonal modes until it reaches a steady state condition. Similarly, when the playing key is released, the sound fades away and during the decay period its harmonic structure again changes. Additionally, during the decay period there is a shifting of the phases of the different partials with respect to one another. These dynamic factors within the organ pipe itself, taken with the fact that a large number of pipes are provided, each of which sounds its tone from a different point in space, result in the highly complex sound pattern which is characteristic of an organ, and which is virtually impossible to duplicate electronically. Even if some of the sounds might be successfully simulated, the electronic means for doing so would involve such high costs that the resultant instrument would probably be more expensive than the pipe organ itself, for such simulation would require an amplifier channel and a loudspeaker for each note in each rank of the organ in order to reproduce the directional effect of the sound from an organ, and would require sophisticated electronics to reproduce as nearly as possible the unique qualities of the pipe itself in shifting from one tone to another as it picks up and fades away.
In spite of the extraordinary and desirable sound produced by pipe organs, they do have certain drawbacks which have limited their usefulness in some applications. One such drawback arises from the fact that with many organs it is extremely difficult to obtain a suitable degree of "expression", or control of the volume of sound produced. On very large organ installations, expression can be obtained in certain degree through the provision of a large number of ranks of pipes with a wide variety of stops which allow the organist to select various registers not only for the quality of sound, but for volume control. Particularly in smaller installations, however, where the number of ranks is limited because of factors such as cost, insufficient space, or the like, but also in some large installations, it has been the practice to provide the desired expression by locating all, or at least some, of the pipe ranks within an enclosed space referred to as a "swell chamber". The swell chamber is, generally speaking, a large, room-sized enclosure that is relatively soundproof on all sides except the one which communicates with the room into which the sound is to be directed, i.e., the listening room. This open side of the swell chamber is closable by means of shutters (usually vertical) which are pivotally mounted so that they can be opened and closed by the organist to vary the volume of the sound projected into the listening space (see, for example, U.S. Pat. No. 500,040 to Skinner and U.S. Pat. No. 2,005,643 to Willis et al.). However, much more than the volume of sound is affected by these shutters; a swell chamber of the foregoing type also has profound effects on the tone quality, so that the changes which the moving shutters produce may be more properly referred to as "swell effects". For example, the opening of the shutters changes the reverberant characteristics of the swell chamber, since these characteristics are different for the chamber by itself than for the chamber attached to the room to which the sound is directed. Furthermore, a dynamic change in these characteristics occurs as the shutters move, the motion of the shutters changing the paths that the sound waves take between the source of the tone and the listeners. Since the organ pipes generally are spread throughout a swell chamber, the path lengths from each pipe to each of the shutter openings are different. These path lengths change as the shutter positions change so that the distance from any given pipe to listener's ear constantly changes as the shutters move, producing Doppler effects and other variations in the sound being heard. The tone quality of the sound produced by a swell chamber also varies because of the greater attenuation of high frequencies than low frequencies when the shutters are closed; similarly, the overall structure of the walls of the swell box, which vibrate more or less in accordance with the frequencies produced by the pipes and the rigidity of the walls, also affects the quality of tone. Thus, the use of a swell chamber and shutters with a pipe organ produces many subtle, highly desirable, dynamic variations in the tone, color and volume of the sound produced by an organ.
However, a serious problem exists with most organ installations in that a properly constructed swell chamber for a large pipe organ is extremely expensive to install, in addition to the fact that it requires a large amount of space within the building which might be used for other purposes. The larger the installation, the more the cost increases, since the requirements for air to operate the pipes move up with the cube of the pipe size. Thus, as the pipes get bigger, larger air blowers become necessary and the larger the blower, the more remote must be its location so that it will not intrude on the sound produced by the pipes. A remote location, however, requires, large and expensive air ducts to be installed. Similarly, the greater the flow of air, the larger are the requirements for air regulators and for tremulant devices, with the end result being an extremely high cost which makes such installations impractical in many cases.
Another difficulty encountered with the use of swell chambers lies in the fact that such chambers are usually substantially closed off from the listening room, particularly when the organ is not in use. As a result, the temperature in a swell chamber can vary over a wide range, and such temperature variations can detune the pipes.
It has also been found that it is very difficult to obtain suitable variations in the sound volume produced by the pipes through adjustment of the shutter positions in typical swell chamber installations, since in general the size of the shutter opening is relatively small with respect to the volume of the chamber. Attempts to improve the expression from such chambers led to various shutter constructions that attempted to obtain the desired range of sound volume by reducing the amount of sound escaping from the chamber when the shutters are closed. A variety of shutter seal designs were developed for this purpose (see, for example, U.S. Pat. Nos. 1,230,165 to Hope-Jones, 1,225,666 to Lockwood, and 2,072,844 to Austin), but this approach was found to be unsatisfactory since attempts to seal the shutters upon closure led to problems of shutter slamming, binding of the shutter mechanism with changes in temperature or humidity, and the like.
In the past, some attempts have been made to simulate organ sounds by placing a small group of organ pipes in a piano housing (see, for example, U.S. Pat. No. 1,835,360 to Waters), in an old-style player piano device such as a nickelodeon, wherein both the piano and the small group of pipes were played from a piano roll, or in a small, portable housing (see U.S. Pat. No. 2,910,907 to Bowman). Occasionally these housings were provided with shutters to control the volume of sound as in the Waters patent, and in general they were constructed with flat, reflective internal surfaces designed to project the sound outwardly. However, these arrangements did not provide true swell chamber simulation, and none were successful in producing a quality musical sound since the placement of such groups of pipes in small housings or boxes of this type resulted in a serious detuning effect on the organ pipes and provided an undesirable coloration of the sounds. Further, they produced an overly "bottled up" sound not entirely attributable to the reduced volume when the housing shutters were closed, and presented problems of air pressure buildup when the shutters were closed.
The detuning and coloration effects produced by such prior devices were not particularly objectionable in the early instruments, since they were almost always used for popular music which would have some form of a vibrato or tremulant. This caused the tones to shift so much that the average pitch was not readily ascertainable to the listener; thus, it did not matter if the pipes were out of tune. However, such detuning is very objectionable in an organ played without tremulant or where the nature of the music is such that even small amounts of detuning would be noticed by the listener, as in a church organ or a concert organ. It was found that the problem of detuning which occurred in the prior devices varied with different pipes and with different positions of the shutters so that a given pipe might be in tune with an opened shutter, be drastically detuned at a half closed shutter, and come back, into perfect tune when the shutter was fully closed, while another pipe might undergo just the opposite effect. The prior art was not able to solve this problem of detuning, and thus the early attempts at providing small enclosures for organ pipes in order to simultate the large organ sound never progressed beyond the state of being a mere novelty.
One prior art attempt to overcome what was perceived as a problem with pipe organs in the lower frequency range resulted in placement of the organ pipes in a soundproof enclosure, and locating a microphone in the enclosure to electronically reproduce the sound. U.S. Pat. No. 2,191,734 to Wick utilized such a system to overcome "peaks and hollows" in the sound produced by various pipes so that a nearly even relative strength and quality is provided. However, such an enclosure is not a swell chamber, and does not produce the desirable effects of a swell chamber, and thus did not represent a solution to the problems presented by large and expensive swell chamber installations.
It has now been found that by proper construction in accordance with the present invention, a compact swell box can be provided which does not have the detuning effect of prior devices and which, therefore, produces the desirable tone characteristics of a swell chamber in a structure that is reduced in size and expense without a corresponding reduction in quality of sound.